The Inner Workings of an Onion

Onions have long been a favourite source of material for microscopists who want to explore the inner workings of a cell. Peel apart the onion bulb scales and it's easy to strip away the skin of cells that coats the scales; mount these in water on a microscope slide and large, brick-shaped translucent cells are easily visible and reveal the nucleus, that contains the DNA and controls the life of the cell. The centre of the cell is occupied by a large fluid-filled vacuole, with cytoplasm squeezed between it and the cell walls. Watch for a while and it soon becomes apparent the the cytoplasm is constantly streaming around the cell walls, carrying with it minute organelles like the mitochondria, they provide the energy that keeps the cells alive. Sometimes the cytoplasm is drawn out in strings across the vacuole, like stretched-out chewing gum. The whole of the cell is in a constant state of motion. So, next time you're about to chop an onion and chuck it in the frying pan, pause for a moment and contemplate the marvellous process shown in these video clips, which is going on in hundreds of thousands of cells in the living onion in your hand.